The present invention is directed to fusion bonding of glass plates, particularly to vacuum fusion bonding of glass plates, and more particularly to an improved apparatus and method for void-free vacuum fusion bonding of glass plates within which are etched features, such as microstructure channels and ports.
Apparatus using a network of fluidic channels, such as microchannel arrays for chemical electrophoresis, involve the formation of the channels on one or both mating glass plates, for example, and the plates are bonded together, such as by fusion bonding. A common problem with fusion bonding is incomplete bonding of the areas, leaving thin, unbonded regions or voids. Even with the use of external force and pressure, voids are difficult to avoid. The concept of developing a partial vacuum between two substrates while maintaining an ambient or higher pressure outside the substrates has been used in mask aligners for some time, and this greatly enhances the area of close contact. The concept of using vacuum and fusion was recently demonstrated on glass, and that process is described and claimed in U.S. application Ser. No. 09/039,522 filed Mar. 16, 1998, now U.S. Pat. No. 6,131,410 issued Oct. 17, 2000, entitled "Vacuum Pull Down for an Enhanced Bonding Process," assigned to the same assignee.
The present invention solves the problem of conveniently applying the vacuum force with an apparatus that is compatible with the high temperatures needed for glass fusion bonding and is potentially useful for very large substrates that are patterned with small features. The present invention eliminates intermediate bonding layers which tend to fill small features etched into the substrates. Thus the present invention provides an improved apparatus and method for vacuum fusion bonding of large, patterned glass plates, such as microstructure channels for chemical electrophoresis.